This invention pertains to the field of antiviral therapy and to peptide chemistry. More particularly, the invention relates to lytic peptides having significant anti-viral activity.
Naturally occurring lytic peptides play an important, if not critical, role as immunological agents in insects, and appear to provide defense functions in a range of other animals as well. These peptides destroy prokaryotic and other non-host cells by disrupting the cell membrane, thereby promoting cell lysis. Common features of these naturally occurring lytic peptides include an overall basic charge, a small size (23-39 amino acid residues), and the ability to form amphipathic xcex1-helices or xcex2-pleated sheets. Another feature found in some lytic peptides is a hydrophobic tail, a non-amphipathic sequence of hydrophobic amino acids of varying length located at one end of the peptide.
Several groups of amphipathic peptides have been identified, including cecropins (originally described in U.S. Pat. No. 4,355,104 and 4,520,016 to Hultmark et al.), defensins, sarcotoxins, melittin, and magainins (described in U.S. Pat. No. 4,810,777 to Zasloff). Each of these groups of peptides is distinguished by sequence and secondary structure characteristics.
The mechanism of peptide-induced cell lysis relies on the ordered secondary conformation and positive charge density of the peptide. Several hypotheses for explaining the mechanism by which these peptides exert their effect have been advanced. For example, the peptides may form ion channels or pores which extend through the cell membrane, and result in osmotically induced cytolysis.
Active synthetic analogs of naturally occurring lytic peptides have been produced and tested in vitro against a variety of prokaryotic and eukaryotic cell types (see for example Arrowood, et al., J. Protozool., 38: 161s (1991); Jaynes, et al., FASEB J., 2: 2878 (1988)), including: gram positive and gram negative bacteria, fungi, yeast, protozoa, and neoplastic or transformed mammalian cells. The studies have demonstrated that synthetic peptide analogs can have higher levels of lytic activity for different types of cells than the naturally occurring peptides. A discussion of lytic peptides, both naturally-occuring and synthetic, can be found in Jaynes, xe2x80x9cLytic peptides, use for growth, infection and cancer,xe2x80x9d WO 90/12866 (incorporated herein by reference). This reference sets out the defining qualities of lytic peptides and sets out several sequences of active synthetic lytic peptides.
The specificity of the peptide action can depend upon the concentration of the amphipathic peptide and the type of membrane with which it interacts. Jaynes, J. M., et al., Peptide Research, 2: 157 (1989) discuss the altered cytoskeletal characteristics of transformed or neoplastic mammalian cells that make them susceptible to lysis by such peptides. Normal, human non-transformed cells remain unaffected at a given peptide concentration, while transformed cells were lysed; however, when normal cells were treated with the cytoskeletal inhibitors cytochalasin D or colchicine, sensitivity to lysis increased. The experiments show that the action of amphipathic peptides on normal mammalian cells is limited. This resistance to lysis was most likely due to the well-developed cytoskeletal network of normal cells. In contrast, transformed cell lines, which have well-known cytoskeletal deficiencies, were sensitive to lysis. Because of differences in cellular sensitivity to lysis, lytic peptide concentration can be manipulated to effect lysis of one cell type but not another at the same situs within an organism.
The virus responsible for AIDS (Acquired Immunodeficiency Syndrome) commonly called HIV (Human Immunodeficiency Virus), is more appropriately called HTLV III for Human T-Cell Leukemia Virus and, thus, is one of several retroviruses that have recently been described as responsible for some types of leukemia. AIDS has been recognized clinically, as a unique syndrome, since 1981. The hallmark of this disease is a quantitative reduction in the T-helper-cell population resulting in a greatly increased sensitivity to infectious disease, with the ultimate outcome of death by opportunistic infection a foreordained consequence of virus infection. The virus contains RNA and, as a retrovirus, possesses several unique enzymes which ultimately allow for the integration of the viral genome into the host""s heredity in a DNA form. The virus can remain xe2x80x9csilentxe2x80x9d for many years until, under certain conditions, the viral genome is activated and infectious virus is produced in massive numbers resulting in the eventual depletion of the victim""s T-helper-cell population. This component of the immune system is integral to fighting the infections that are encountered on a daily basis. HIV infection is very difficult to treat due in part to its highly variable and mutable coat characteristics, which make traditional vaccine treatment ineffective.
The present invention relates to a method for treating animals infected with a retrovirus or enveloped virus. The method comprises treating the infected animal with a lytic peptide at concentrations that are lethal to virus or virus-infected cells, yet are sub-lethal to healthy cells. A further embodiment of this invention is the treatment of a retrovirus or enveloped virus-infected animal with a dose of lytic peptide that is sub-lethal to the virus or virus-infected cells, but results in the infected cell producing virus particles that are non-infective.